In general, the lower the engine load, the worse the heat efficiency, so at the time of engine low load operation, the mechanical compression ratio ((top dead center cylinder volume+stroke volume)/top dead center cylinder volume) is preferably raised to raise the expansion ratio and thereby improve the heat efficiency. For this, it has been known to make the cylinder block and crankcase move relative to each other to change the distance between the cylinder block and the crankshaft and thereby make the mechanical compression ratio variable.
In a V-type internal combustion engine, it has been proposed to make the cylinder block parts of the two cylinder groups move relatively to the crankcase separately along the cylinder centerlines of the cylinder groups, but it is difficult to make different cylinder block parts move relatively to the crankcase by a single link mechanism (or cam mechanism). A pair of link mechanisms (or cam mechanisms) becomes necessary for each cylinder block part, so overall two pairs of link mechanisms end up becoming necessary.
To reduce the number of link mechanisms, a variable compression ratio V-type internal combustion engine has been proposed which joins the cylinder blocks of two cylinder groups and makes the joined cylinder block move relatively to the crankcase by a pair of link mechanisms (refer to Japanese Unexamined Patent Publication No. 2005-113743).